There are various types of color displays, and they have become practical. Thin displays are roughly classified into self-emitting displays, such as PDP (plasma display panel), and non-luminescent displays exemplified by LCD (liquid crystal display). A known LCD, which is a non-luminescent display, is a transmissive-type LCD having a backlight on a rear side of the liquid crystal panel.
FIG. 13 is a sectional view showing a common configuration of the transmissive-type LCD. The transmissive-type LCD has a backlight 110 on a rear side of a liquid crystal panel 100. The liquid crystal panel 100 is configured in such a manner that a liquid crystal layer 103 is provided between a pair of transparent substrates 101 and 102, and polarizers 104 and 105 are provided on outer sides of the transparent substrates 101 and 102, respectively. Further, a color filter 106 is provided in the liquid crystal panel 100 so that color displays become available.
Although not illustrated, an electrode layer and an alignment layer are provided inside of the transparent substrates 101 and 102. Voltage to be applied to the liquid crystal layer 103 is controlled so that the amount of light passing through the liquid crystal panel 100 is controlled on a pixel-to-pixel basis. Specifically, the transmissive-type LCD controls light from the backlight 110 in such a manner that the amount of light that is to pass through is controlled at the liquid crystal panel 100, thereby controlling displays.
The backlight 110 emits light that contains wavelengths of three colors RGB necessary for color displays. In combination with the color filter 106, respective RGB are adjusted in transmissivity of light, whereby it becomes possible to determine luminance and hue of the pixels arbitrarily. White-color light sources, such as Electro-luminescence (EL), cold-cathode fluorescent lamps (CCFL), and light emitting diodes (LED) are commonly used as the backlight 110.
As shown in FIG. 14, plural pixels are arranged in matrix in the liquid crystal panel 100. Each of the pixels is generally constituted of three subpixels. The respective subpixels are disposed so as to correspond to filter layers red (R), green (G), and blue (B) in the color filter 106, respectively. Hereinafter, the subpixels will be referred to as a subpixel R, a subpixel G, and a subpixel B, respectively.
Respective subpixels R, G, and B selectively transmit, out of white-color light emitted from the backlight 110, the light having the corresponding wavelength band (i.e. red, green, blue), and absorbs the light having other wavelength bands.
In the transmissive-type LCD of the foregoing configuration, the light emitted from the backlight 110 is controlled in such a manner that the amount of light that is to pass through is controlled at each pixel of the liquid crystal panel 100. This naturally causes some of the light to be absorbed by the liquid crystal panel 100. Further, respective subpixels R, G, and B in the color filter 106 also absorb, out of the white-color light emitted from the backlight 110, the light having a wavelength band other than the corresponding wavelength band. Since the liquid crystal panel and the color filter absorb a great amount of light, the use of the light emitted from the backlight becomes less efficient. Accordingly, a common transmissive-type LCD has the problem of increase in power consumption of the backlight,
The use of an active backlight by which luminance of light emitted is adjustable according to an image displayed is known as a technique that reduces the power consumption of transmissive-type LCD (e.g. Japanese Unexamined Patent Publication No. 65531/1999 (Tokukaihei 11-65531 (published on Mar. 9, 1999)).
Specifically, Publication No. 65531/1999 discloses the technique that reduces the power consumption of the backlight by employing an active backlight by which the luminance is adjustable, and controlling the liquid crystal panel and the active backlight in transmissivity and in luminance, respectively, thereby controlling displays (luminance control) shown on the LCD.
In Publication No. 65531/1999, the luminance of the backlight is controlled so as to match the greatest luminance in the input image (input signal). Further, the transmissivity of the liquid crystal panel is adjusted according to the current luminance of the backlight.
At this time, a transmissivity of a subpixel that is the highest value in the input signal is 100%. Further, the transmissivities other than the highest value, which transmissivities are obtained by calculation on the basis of the backlight value, are 100% or below each. This makes it possible to darken the backlight if the image is dark overall, whereby the power consumption of the backlight is reduced.
Accordingly, in Publication No. 65531/1999, the brightness of the backlight is restrained to a minimum necessary brightness on the basis of the input signals RGB of the input image, and the transmissivity of the liquid crystal is increased by the amount equal to that by which the backlight is darkened. This makes it possible to reduce the amount of light absorbed by the liquid crystal panel, whereby the power consumption of the backlight is reduced.
With the foregoing conventional configuration, the amount of light absorbed by the liquid crystal panel is reduced so that the power consumption of the backlight is reduced. However, the amount of light absorbed by the color filter is not reducible with the conventional configuration. If it becomes possible to reduce the amount of light absorbed by the color filter, the power consumption is reduced further.